Frequency Division Multiplexing for a Multi-Sensor Wireless Telemetry System
Our System acquires several different sensor inputs, FM modulates each level by manipulating Direct Digital Synthesis increment values, transmits the resulting signal on a commercial FM radio band, and receives and decodes the original sensor levels.
Gus Lott, Maruthi Narayanan - 2005

ECE 476 Final Project
Introduction | High Level Design | Program/Hardware | Design Results | Standards & Regulations | Conclusions ]
[Commented Firmware | Commented MATLAB Software | PCB Schematics | Price List | Group Task Breakdown ]
[ Audio Examples (.wav) ]


The problem of encoding multiple input signals into a finite bandwidth space is one that is common in engineering problems today. It is found in communication system encoding schemes from cell phones to cable TV. The problem is that the system needs to carry several independent signals over a single communications medium. Some examples of data encoding for these data communication problems include time division multiplexing (i.e. telephone lines), code division multiplexing (cell phones), statistical multiplexing (internet), and frequency division multiplexing (cable TV).

We have designed a wireless telemetry system that utilizes frequency division multiplexing (FDM) to encode several input sensor values onto a single analog channel for transmission. By using a single transmitter, we can simplify design and reduce bandwidth consumption and power costs. We have encoded three-axis accelerometer data using our technique. Direct digital synthesis (DDS) was utilized to convert three separate ten bit number intro three orthogonal frequencies. A linear combination of these orthogonal signals was FM modulated into the commercial FM band. We also have developed a decoding scheme which reconstructs the original input levels.

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High Level Design

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Program & Hardware Design

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Results of the Design

  • Usability

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    Standards & Regulations
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    Audio Examples

    The following files are examples of what the output sounds like when the system is accelerated in each direction. Each of these audio files were created while oscillating the board back and forth in my hand.

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    Price List
    ComponentUnit PriceQuantity
    X-Y Axis Accelerometer +10g
    Freescale MMA6231Q
    Z Axis Accelerometer +8g
    Freescale MMA1220D
    Atmel MEGA32L$8.281
    D/A convertor @3.3V and 10-bitsSample
    Voltage Controlled oscillator with FM tuning pin
    Dallas Semiconductor MAX2606
    Voltage Regulator
    Texas Instruments 3.3V regulator at 500mA
    Voltage Regulator
    Texas Instruments 5V regulator at 50mA low dropout
    8 MHZ Crystal$0.581
    Printed Circuit BoardFree space used on a board from an unrelated project
    Various resistors/capacitors/inductors and potentiometers<$10.00

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    Group Task Breakdown
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